There exist a number of different mobility protocols employed in Release 8 of the 3rd Generation Partnership Project (3GPP) core network. Mobility management in such a telecommunications network generally falls into two categories, one being host-based mobility management and the other being network-based mobility management.
An example of host-based mobility management is Mobile Internet Protocol (MIP, or Mobile IPv6). Mobile IP allows location-independent routing of IP packets on a data network, such as the Internet. Each mobile device (i.e. mobile node) is identified by its home address disregarding its current location in the Internet. While away from its home network, a mobile node is associated with a care-of address which identifies its current location, and its home address is associated with the local endpoint via a tunnel to its home agent (see definition below). Mobile IP specifies how a mobile node registers with its home agent and how the home agent routes packets to the mobile node through the tunnel.
FIG. 1 shows a basic overview of a Mobile IP network, having a home network 1 and a foreign network 3. The home network 1 of a mobile node 5 is the network within which the mobile node 5 receives its identifying IP address (known as the home address). The home address of a mobile node 5 is the IP address assigned to the mobile node 5 within its home network 1. A foreign network 3 is the network in which a mobile node 5 is operating when away from its home network 1 (as shown in FIG. 1).
The care-of address of a mobile node 5 is the physical IP address of the node when operating in the foreign network 3. A Home Agent (HA) 7 is a router in the home network 1 of a mobile node 5, which tunnels packets for delivery to the mobile node 5 when it is away from its home network 1. The HA 7 maintains current location information (IP address information) for the mobile node 5, and is used with one or more Access Routers (ARs) 9. An AR 9 is a router that stores information about mobile nodes 5 visiting the associated foreign network 3. ARs 9 also advertise care-of-addresses which are used by Mobile IP. The association of the home address with a care-of address is called a “binding”. The HA 7 routes packets to the AR 9 via a tunnel 11, the AR 9 in turn forwarding packets to the mobile node 5.
In contrast to host-based mobility management, an example of network-based mobility management is the GPRS Tunneling Protocol (GTP). Another example of network-based mobility management is Proxy Mobile IP (PMIP, or Proxy Mobile IPv6), which is a new standard being developed by the Internet Engineering Task Force (IETF).
To help explain these network-based mobility management protocols further, reference will now be made to FIG. 2 which shows a more detailed overview of an exemplary telecommunications network, known as the E-UTRAN (Evolved UMTS terrestrial radio access network) which uses the Long Term Evolution (LTE) standard. The network comprises a plurality of radio base stations (also known as eNodeBs, Node Bs, etc) 21a, 21b, 21c, each of which maintains one or more cells (not illustrated). User Equipment (“UE”, i.e. mobile equipment or mobile nodes) 23a, 23b, 23c, 23d within each cell communicate with the corresponding eNodeB 21 of that cell.
In the E-UTRAN, eNodeBs 21 are capable of communicating with one another over interfaces known as X2 interfaces (illustrated as dashed lines in FIG. 2). Each eNodeB 21 further has one or more interfaces with the core network. These are known as S1 interfaces. In particular, the eNodeBs 21 have one or more S1 interfaces to one or more mobility management entities (MMEs) 25a, 25b, which will be described in more detail below.
The telecommunications network also comprises a Serving Gateway (SGW) 29. The Serving Gateway 29 is connected to an eNodeB 21a via an S1u interface, and an MME 25a via an S11 interface. It will be appreciated that a Serving Gateway 29 may be connected to one or more of each of said devices, plus other nodes such as Serving GPRS Support nodes (SGSNs, not shown). A Serving Gateway 29 is adapted to perform, amongst other things, the routing and forwarding of user data packets, while also acting as the mobility anchor for the user plane during inter eNodeB handovers (for example as a UE 23a is handed over from eNodeB 21a to eNodeB 21c). The Serving Gateway 29 also acts as the anchor for mobility between LTE and other 3GPP technologies. It also manages and stores UE contexts, for example parameters of the IP bearer service, and network internal routing information.
The Serving Gateway 29 is connected to a Packet Data Network Gateway (PDN GW) 31 via an S5 interface. The PDN GW 31 provides connectivity to the UE to external packet data networks, such as the internet 33, by being the point of exit and entry of traffic for the UE.
The MME 25a is responsible, amongst other things, for idle mode UE tracking and paging procedures. It is also involved in a bearer activation/deactivation process and is also responsible for choosing the initial Serving Gateway (SGW) for a UE.
As mentioned above, a PDN GW 31 provides connectivity (via an SGi interface) from the UE 23 to external packet data networks 33 (for example the internet) by being the point of exit and entry of traffic for the UE 23. A UE 23 may have simultaneous connectivity with more than one PDN GW 31 for accessing multiple PDNs 33. The PDN GW 31 performs, amongst other things, policy enforcement, packet filtering for each user, charging support, lawful Interception and packet screening. Another key role of the PDN GW 31 is to act as the anchor for mobility between 3GPP and non-3GPP technologies, via S2 interfaces (not shown).
Mobility management in a Proxy Mobile IP system defines two network entities which are involved in the process, a Local Mobility Anchor (LMA) and the Mobile Access Gateway (MAG), as defined by the Proxy Mobile IP protocol RFC 5213. When applied to the S5 interface of the 3GPP architecture of FIG. 2, the SGW 29 acts as a MAG while the PDN GW 31 acts as a LMA. The MAG is a function on an access router that manages the mobility related signalling for a mobile host that is attached to its access link. LMA is the home agent for the mobile host in a Proxy Mobile IP domain. The protocol works as follows:                A mobile host enters a PMIP domain        A Mobile Access Gateway on that link checks host authorization        A mobile host obtains an IP address        A Mobile Access Gateway updates a Local Mobility Anchor about the current location of a host        Both MAG and LMA create a bi-directional tunnel.        
Network-based mobility management offered by GTP and PMIP provide similar functionality to that of Mobile IP. However, network-based mobility management does not require any modifications to the network stack of the mobile host. In other words, the mobility is taken care of, as the name suggests, by the network.
A key functional difference between GTP and PMIP, however, is that the former also supports the establishment of sub-sessions within a mobility session, known as “bearers”, (or “PDP contexts” in older versions of the 3GPP standard). Bearers enable Quality-of-Service (QoS) differentiation to be provided by using centralized traffic classification. As a consequence, downlink packets need to be classified and assigned to a particular QoS class (known as “mapping to a bearer” in the 3GPP standard) only in an anchor point (for example, in a PDN Gateway 31 as shown in FIG. 2). Bearers can be thought of as L2 channels between a UE 23 and the first-hop router (i.e. PDN GW 31) with different QoS properties. When a new bearer is set up the PDN GW 31 and the UE agree on which IP micro-flows (i.e. Service Data Flows, SDFs, as explained further below), identified by a 5-tuple, are placed on the new bearer. Thus all packets sent by the PDN GW 31 to the UE (or vice versa) are classified to see which bearer(s) the packets should be placed on. This classification is carried out by looking through these 5-tuple values and comparing them to the header fields in the packet. Later elements on the path of the packet (for example the SGW 29, eNodeB 21) do not have to classify again, since they already know which bearer the packet is on and consequently what QoS to apply.
FIG. 3 shows the relationship between Service Data Flows (SDFs) and bearers in a LTE telecommunications network. A service data flow is a set of IP packets matching a certain 5-tuple filterset. In other words, a SDF is a portion of the traffic, while a bearer is a transmission facility. The SDFs are placed onto (or transmitted through or via) bearers. A bearer is itself a virtual connection having an unique Quality-of-Service (QoS) class.
In FIG. 3 a first bearer 301 having a first QoS class (QoS1) is shown as carrying a plurality of Service Data Flows SDF11 to SDF1N, while a second bearer 303 having a second QoS class (QoS2) is shown as carrying a plurality of Service Data Flows SDF21 to SDF2N. In the network of FIG. 2, a bearer on a data path between a UE 23 and a PDN Gateway 31 will have three segments:                a radio bearer between an UE 23a and an eNodeB 21a,         a data bearer between the eNodeB 21a and the SGW 29, the S1u bearer, and        a data bearer between the SWG 29 and the PDN GW 31, the S5 bearer.        
Since a packet is classified and assigned to a particular QoS class, the packet is then marked accordingly. In particular, the bearer is identified by a Tunnel Endpoint Identifier (TEID), which tells the result of the classification to all subsequent nodes in the network (as described above). The TEID is used to identify which bearer the packet travels on only over the S1u and S5 interfaces, where the GTP protocol is used to carry packets. Different fields/mechanisms (i.e. radio related identifiers) are used over the air interface, where GTP is not used to carry packets.
For uplink packets, the mobile node performs classification and bearer mapping, and all subsequent nodes can rely on this classification (with one node actually verifying it), for the purpose of network control.
It is noted, however, that the PMIP based solution does not comprise bearer capability (i.e. cannot establish bearers), and instead requires packet classification to be carried out both in the PDN GW 31 and in a Serving Gateway 29. To achieve packet classification, a Policy and Charging Rules Function (PCRF) must download the classification rules to the Serving Gateway 29 (i.e. in addition to the PDN GW 31 shown in FIG. 2). Furthermore, the policy rules must also be downloaded to a new Serving Gateway following a change of Serving Gateway, for example due to a handover. This has the disadvantage of resulting in excessive policy related signaling and makes the policy system mobility-aware.
Currently, Mobile Internet Protocol (MIP), also known as Client Mobile Internet Protocol (CMIP), is the only host-based mobility protocol considered for general use for non-3GPP accesses. Similar to PMIP, it lacks bearer capabilities, and therefore has the disadvantage of requiring flow classification in the gateway of the non-3GPP access. In other words, a control node must look into a CMIP tunnel for the purpose of flow classification. However, this is not possible if the CMIP tunnel is encrypted.